As indicated in U.S. Pat. No. 4,078,286, in a typical process for electrophotographic duplication, a light image of an original to be copied is recorded in the form of a latent electrostatic image upon a photosensitive member, and the latent image is subsequently rendered visible by the application of electroscopic particles, which are commonly referred to as toner. The visible toner image is then in a loose powdered form and it can be easily disturbed or destroyed. The toner image is usually fixed or fused upon a support, which may be the photosensitive member itself or another support such as a sheet of plain paper. The present invention relates to the fusing of the toner image upon a support.
In order to fuse electroscopic toner material onto a support surface permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky. This heating causes the toner to flow to some extent into the fibers or pores of the support member. Thereafter, as the toner material cools, solidification of the toner material causes the toner material to be firmly bonded to the support.
The use of thermal energy for fixing toner images onto a support member is well known. Several approaches to thermal fusing of electroscopic toner images have been described in the prior art. These methods include providing the application of heat and pressure substantially concurrently by various means: a roll pair maintained in pressure contact; a flat or curved plate member in pressure contact with a roll; a belt member in pressure contact with a roll; and the like. Heat may be applied by heating one or both of the rolls, plate members or belt members. The fusing of the toner particles takes place when the proper combination of heat, pressure and contact time are provided. The balancing of these parameters to bring about the fusing of the toner particles is well known in the art, and they can be adjusted to suit particular machines or process conditions.
During operation of a fusing system in which heat is applied to cause thermal fusing of the toner particles onto a support, both the toner image and the support are passed through a nip formed between the roll pair, or plate or belt members. The concurrent transfer of heat and the application of pressure in the nip effects the fusing of the toner image onto the support. It is important in the fusing process that no offset of the toner particles from the support to the fuser member takes place during normal operations. Toner particles offset onto the fuser member may subsequently transfer to other parts of the machine or onto the support in subsequent copying cycles, thus increasing the background or interfering with the materials being copied there. The so called "hot offset" occurs when the temperature of the toner is raised to a point where the toner particles liquify and a splitting of the molten toner takes place during the fusing operation. "Cold offset" may be caused, even at the temperatures below the molten point of the toner, by such factors as imperfections in the surface of the fusing members; by the toner particles being insufficiently adhering to the support; by electrostatic forces which may be present; etc.
Another problem frequently encountered in fusing with a heated member is that the substrate, e.g. a sheet of paper, on which the toner image is fused may curl and/or adhere to the heated fuser. Such adhering paper will tend to wrap itself around the fuser and thus prevent the fuser from performing its intended operations in subsequent copying cycles. Such adhering paper must be generally removed by hand, resulting in much manual labor and machine downtime.
As indicated in said U.S. Pat. No. 4,078,286, it is known in the prior art to provide the heated member in a fusing system with a covering of a heat-resistant, release material on its outer surface. Coupled to such a heated member is a backup or pressure member covered with a heat-resistant, flexible material. The nip is formed by the flexible material under pressure contact with the heated member. Examples of the heat resistant, release materials for the fuser members include polytetrafluoroethylene, silicone rubber, fluorocarbon elastomers and the like. A suitable offset preventing liquid may be used on the fuser member to minimize or avoid "offsetting." Silicone oils are widely used as the offset preventing or release agent. The pressure member may be made of such materials as silicone rubber and polyfluoroethylenepropylene.
Both said U.S. Pat. No. 4,078,286 and U.S. Pat. No. 4,064,313 relate to the use of silicone rubber as a coating material on a fuser member and the problem of adhering the coating of the silicone rubber to the base member to prevent the separation of the silicone rubber coating from the base member.
In U.S. Pat. No. 3,809,854, there is disclosed a composite article useful as a fuser blanket which is made of a dimensionally stable substrate having bonded to one surface thereof an electrically conductive layer of a resiliently compressible elastomer, and a thin resiliently compressible silicon elastomer outer layer bonded thereto. Examples of the electrically conductive resiliently compressible elastomer include a peroxide cured vinyl methyl polysiloxane polymer containing therein an antistatic or conductive material such as a peroxide curable carbon black filled polysiloxane. The thin resiliently compressible silicone elastomer outer layer may be made of the cured or further polymerized product of a silicone gum such as a dimethyl vinyl polysiloxane.
Canadian Pat. No. 658,954 discloses a method of preparing silicone rubber compositions which comprise an essentially water free mixture of a hydroxyl endblocked diorganosiloxane polymer, a crosslinking agent, a crosslinking catalyst and optionally an essentially anhydrous filler. Aside from other differences in the composition of the present invention and that of the Canadian patent, the fillers there are entirely different from those of the present invention. The compositions of the Canadian patent are intended for use as sealants, electrical insulations, coatings, dental cement, etc.
U.S. Pat. No. 3,231,572 discloses a process for rapid curing at ambient temperature of organopolysiloxanes. The composition of this patent comprises a mixture of hydroxyl terminated diorganopolysiloxane, a crosslinking agent, fillers, and an accelerator which is made of an organic derivative of tin in combination with a mono-, di- or trichloracetic acid. The mixture so prepared is intended for use as caulking, coating, lining, etc.
U.S. Pat. No. 3,795,033 discloses a roll for fusing toner images to a sheet, which has coated on its exterior surface a mixture of a silicone gum, fillers, and a curing agent.
In U.S. Pat. No. 3,848,305 there is disclosed a fuser roll coated with a silicone elastomer, which is made of a polydimethyl siloxane, a trifunctional silane, silicon dioxide, and ferric oxide. A dibutyltin dilaurate catalyst is also used in preparing the elastomer.
Finally, in U.S. Pat. No. 4,074,001, there is disclosed a fixing roll for electrophotography having a surface layer made of a diorganopolysiloxane having silanol groups at the molecular terminals, a diorganopolysiloxane having trialkylsilyl groups at the molecular terminals, an alkoxy-containing silane, a metal salt of an organic acid as the crosslinking catalyst, a powdery calcium carbonate, iron oxide, and titanium dioxide.
While the prior art fusers have been effective in providing the fusing of thousands of copies between servicing and/or replacement of the fuser member, there is a continuing need to improve the life of the fusing member, the copy quality resulting from the fusing operation, and the release properties of the fusing member.
Accordingly, it is an object of the invention to provide an improved fusing member for use in an electrostatographic copying machine.
It is another object of the present invention to provide a fusing member which yields high quality copies, extended life cycles, as well as possessing superior release properties.
It is still another object of the invention to provide a novel fuser member suitable for use in a cold pressure fixing apparatus.